It is proposed to further develop and refine models representing a simulated human head and neck when this system is subjected both to impact on the head and also when loaded impulsively to simulate sudden deceleration of a torso. A comprehensive investigation of this problem has been undertaken both experimentally and analytically by the proposed investigator; some significant results have already been obtained and the fulfillment of the general objectives, to be accomplished within the next year, will lead to the first definitive quantitative information on stresses, strains and displacements in such a system under controlled dynamic loading. However, the model selected is only a first-order mechanical device for the study of this hyperextension problem. The present proposal is a request to extend the course of the investigation for a period of three years for the purpose of permitting the construction of more detailed models of the system. At the present time, the vertebral structure and its musculature have been replicated by means of artificial materials, and corresponding analytical models have been developed. However, the tests conducted thus far indicate that a duplication of the composite motion of which the neck is capable, i.e. simultaneous saggital motion and rotation about axes either perpendicular to this plane or about the vertical, or else a combination of such motions, will require a considerably more sophisticated model. Thus a second-order model will be built and subjected to impacts and impulsive loadings under realistic conditions. Particular attention will be devoted to applications with respect to protective environnments; the possible deleterious effect on hyperextension resulting from the presence of a helmet will be investigated. A continuum analytical representation of the event will be developed.